Pour the can of beans into a colander and rinse with cool water. Allow the excess water to drain off. Drain the can of tuna. Combine the drained beans and tuna in a bowl. Thinly slice the green onions and add to the bowl as well.
Add the olive oil and lemon juice to the bowl, along with a light sprinkle of salt and freshly ground black pepper. Stir to combine.
Taste the mixture and add salt, pepper, or lemon juice to your liking.